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Hindawi Publishing CorporationEURASIP Journal on Applied Signal Processing Volume 2006, Article ID 69217, Pages 1 3 DOI 10.1155/ASP/2006/69217 Editorial Implementation Aspects and Testbe

Hindawi Publishing Corporation

EURASIP Journal on Applied Signal Processing

Volume 2006, Article ID 69217, Pages 1 3

DOI 10.1155/ASP/2006/69217

Editorial

Implementation Aspects and Testbeds for MIMO Systems

Thomas Kaiser, 1 Andr ´e Bourdoux, 2 Markus Rupp, 3 and Ulrich Heute 4

1 Department of Communication Systems, Faculty of Engineering, University of Duisburg-Essen, 47048 Duisburg, Germany

2 IMEC vzw, DESICS Division, Kapeldreef 75, 3001 Leuven, Belgium

3 Institute of Communications and RF Engineering, TU Wien, Gusshausstrasse 25/389, 1040 Wien, Austria

4 Institute for Circuits and Systems Theory, Faculty of Engineering, Christian-Albrechts-University Kiel, Kaiserstraße 2,

24143 Kiel-Gaarden, Germany

Received 21 September 2005; Accepted 21 September 2005

Copyright © 2006 Thomas Kaiser et al This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

The MIMO (multiple-input multiple-output) systems have

emerged as a key technology for wireless local area networks

(WLANs), wireless metropolitan area networks (WMANs),

and cellular mobile communication systems (3G, 4G)

be-cause they promise greater coverage, higher data rates, and

improved link robustness by adding a spatial dimension

to the time, the frequency, and the code dimensions

Re-cent progress in standardization and in first MIMO

pro-totype chipsets has forced manufacturers worldwide to pay

more attention to MIMO implementation aspects Moreover,

MIMO testbeds have become more and more attractive to

universities and to research institutes as has been observed

in the past few years The aim of this special issue is to

re-flect the current state-of-the-art MIMO testbeds and to

ex-amine the several MIMO implementation challenges for

cur-rent and for future wireless communication standards

We classified the accepted thirteen submissions into four

major categories: (1) hardware-oriented prototypes, (2)

flex-ible testbeds, (3) analog issues, and (4) fast algorithms

Hardware-oriented prototypes

In the first paper, Guo et al present an efficient circulant

approximation-based MIMO equalizer architecture for the

CDMA downlink, reducing the direct matrix inverse (DMI)

to some FFT operations Further parallel and pipelined VLSI

architectures with Hermitian optimization and

reduced-state FFT reduce the complexity even more A

compara-tive study of both the conjugate-gradient and the DMI

algo-rithms shows very promising performance/complexity

trade-off VLSI design space in terms of area/time efficiency is

explored extensively for layered parallelism and pipelining

with a Catapult C high-level synthesis methodology In the next paper, Dowle et al describe the development of the STAR (space-time array research) platform, an FPGA-based research unit operating at 2.45 GHz and capable of having

a maximum of twelve 20 MHz bandwidth channels of real-time, space-real-time, and MIMO processing The design method starts with Matlab/Octave With manual refinement steps, VHDL code for FPGAs is obtained and verified via ModelSim with the original design Various pitfalls associated with the implementation of MIMO algorithms in real time are high-lighted, and finally the development requirements are given

to aid comparison with traditional DSP development The paper by Goud et al describes a portable 4×4 MIMO test-bed operating in an ISM band around 900 MHz Details of channel measurements and capacity analysis of unusual in-door and outin-door locations obtained with the test-bed are also included The next paper by Haustein et al presents a re-configurable hardware test-bed suitable for real-time mobile communication with multiple antennas Supported are four transmit and five receive antennas operating at 5.2 GHz with

a maximum bandwidth of 100 MHz Efficient implementa-tion of MIMO signal processing using FPGAs and DSPs is described An experimental verification of several real-time MIMO transmission schemes at high data rates in a typical

office scenario is presented, and results on the achieved BER and throughput performance are given Spectral efficiencies

of more than 20 bps/Hz and a throughput of more than

150 Mbps was shown with a single-carrier transmission The experimental results clearly show the feasibility of real-time high-data-rate MIMO techniques with state-of-the-art hard-ware and that more sophisticated baseband signal processing will be an essential part of future communication systems

2 EURASIP Journal on Applied Signal Processing

Weijers et al propose a systematic way from a

transmission-system model, as often underlying a Matlab simulation, to a

real-time prototype realized on a predefined hardware

plat-form, avoiding inconsistencies of adhoc procedures The

sug-gested design flow is partly manual, but always systematic

and assisted by tools suitable for the individual steps

Flexible testbeds

The next five papers of the issue cover flexible testbeds,

where the flexibility is usually achieved by higher-level

pro-gramming languages Xiang et al describe a 4×4

MIMO-OFDM test-bed mainly based on laboratory test equipment

and offline processing Channel measurements and antenna

selection techniques are presented The paper also assesses

the degradation due to carrier frequency offset and

imper-fect channel estimation The next paper by Borkowski et al

presents a real-time MIMO test-bed for both single-carrier

and OFDM transmission A specific SIMD processor

imple-mented on FPGAs is described, as well as the specific analog

hardware at 10 GHz that is supported by offline and online

calibration The influence of polarization on the channel

ca-pacity is also addressed In the paper by Caban et al., the

fo-cus is on the comfortable use of a flexible DSP/FPGA and RF

hardware setup Real-time tests with four transmit and

re-ceive channels each are possible at a data rate of 2.45 GHz

All pre- and postprocessing is done within Matlab, while the

real-time requirements are fulfilled by burst-data

transmis-sion through the hardware Multiuser abilities are also

pro-vided In the contribution by Samuelsson et al., a test-bed for

spatial multiplexing is proposed that relies on off-the-shelf

radio hardware only A comparison of SISO with MIMO

re-veals that even with rather low-cost hardware the

remark-able spectral efficiency improvement and the associated

mul-tiplexing gain of MIMO can be demonstrated The paper by

F`abregas et al presents the complete design methodology of

a MIMO-OFDM test-bed for WLAN applications The

de-sign steps include a characterization of the indoor MIMO

channel and the specific baseband and RF hardware at 5 GHz

The mapping and validation of the algorithms using

Mat-lab, C++, and VHDL is detailed, and measurements are

de-scribed

Analog issues

The contribution by Liu et al addresses a specific problem

in the popular transmit-antenna diversity scheme termed

“transmit MRC.” While symmetries are usually assumed for

the up- and downlink channels as well as between the

anten-nas, in reality mismatches are found A novel statistical

anal-ysis provides a deeper understanding and especially leads to a

novel calibration scheme, which is finally implemented on a

real-time prototyping platform The paper by Piechocki et al

presents an extension of analogue turbo decoder concepts to

MIMO detection The first analogue implementation results

show reductions of a few orders of magnitude in the number

of required transistors, consumed energy, and the same order

of improvement in processing speed LDPC is used as a test

case for the analysis

Fast algorithms

Safar et al propose an efficient detection of space-frequency block codes by means of the sphere decoding technique for-mulated in the complex domain Three approaches are de-tailed: one approach is modulation independent, whereas the two others are specific for QAM and QPSK, respectively The complexity analysis of these techniques is assessed

ACKNOWLEDGMENTS

We thank the authors, the reviewers, the publisher, and the Editor-in-Chief for their efforts We also hope that this spe-cial issue will stimulate subsequent contributions on MIMO testbeds so as to widely spread the required technical knowl-edge and to validate in further detail the realistic perfor-mance gain of multiantenna systems

Thomas Kaiser Andr´e Bourdoux Markus Rupp Ulrich Heute

Thomas Kaiser received a Diploma

de-gree from the Ruhr-University Bochum in

1991, and a Ph.D degree in 1995 and a German Habilitation degree in 2000, both from Gerhard-Mercator-University Duis-burg and in electrical engineering From

1995 to 1996, he spent a research leave

at the University of Southern California, Los Angeles, which was grant-aided by the German Academic Exchange Service From April 2000 to March 2001, he was the Head of the Department

of Communication Systems at Gerhard-Mercator-University Duis-burg and from April 2001 to March 2002, he was the Head of the Department of Wireless Chips & Systems (WCS) at Fraunhofer Institute of Microelectronic Circuits and Systems Now he is the Coleader of the Smart Antenna Research Team (SmART) at the University of Duisburg-Essen In summer 2005, he joined Stan-ford’s Smart Antenna Research Group (SARG) as a Visiting Profes-sor He has published more than 80 papers in international journals and at conferences, and he is the coeditor of the three forthcoming

books: UWB Communication Systems—A Comprehensive Overview, Smart Antennas—State of the Art (both to appear in the EURASIP book series), and UWB Communications (to be published by

Wi-ley) He is the founder of PLANET MIMO Ltd and belongs to the Editorial Board of EURASIP Journal of Applied Signal Processing and to the advisory board of a European multiantenna project He

is the founding Editor-in-Chief of the upcoming IEEE Signal Pro-cessing Society e-letter He is involved in several national and inter-national projects, and has chaired and cochaired a number of spe-cial sessions on multiantenna implementation issues Beside this special issue in hand, he is also a Guest Editor of the EURASIP special issues on “Advances in Smart Antennas,” “UWB State of the Art,” and “Wireless Location Technologies and Applications.” His current research interest focuses on applied signal processing with emphasis on multiantenna systems, especially its applicability

to ultra-wideband systems, and on implementation issues

Thomas Kaiser et al 3

Andr´e Bourdoux received the M.S degree

in electrical engineering (specialization in

microelectronics) in 1982 from the

Univer-sit´e Catholique de Louvain-la-Neuve,

Bel-gium He is coordinating the research on

multiantenna communications in the

Wire-less Research Group at IMEC His current

interests span the areas of wireless

com-munications theory, signal processing, and

transceiver architectures with a special

em-phasis on broadband and multiantenna systems Before joining

IMEC, his research activities were in the field of algorithms and RF

architectures for coherent and high-resolution radar systems He

is the author and coauthor of several conference and journal

pa-pers and of 2 patents applications in the field of SDMA and MIMO

transmission He is a coeditor of the book Smart Antennas—State

of the Art to be published in the EURASIP Book Series on Signal

Processing and Communications

Markus Rupp received his Dipl.-Ing

de-gree in 1988 from the University of

Saar-bruecken, Germany, and his Dr.-Ing

de-gree in 1993 from the Technische

Univer-sit¨at Darmstadt, Germany He is presently

a Full Professor of digital signal processing

in mobile communications at the Technical

University of Vienna He is an Associate

Ed-itor of IEEE Transactions on Signal

Process-ing, of JASP EURASIP Journal of Applied

Signal Processing, of JES EURASIP Journal on Embedded Systems,

and is elected AdCom Member of EURASIP He authored and

co-authored more than 180 papers and patents on adaptive filtering,

wireless communications, and rapid prototyping

Ulrich Heute was born in 1944 in

Magde-burg, went to school till 1964, and

stud-ied electrical engineering at Stuttgart

Tech-nical University from 1965 to 1970; he

re-ceived the Dipl.-Ing degree in 1970 At

Friedrich-Alexander University, Erlangen,

he did research on digital filters, spectral

analysis, and speech processing; he received

the Ph.D degree in 1975 and the

Habilita-tion degree in 1982, and was a Senior

Engi-neer until 1987 He became a Professor for digital signal processing

at Ruhr-University Bochum in 1987, and has been a Professor for

circuit and system theory at Christian-Albrechts University, Kiel,

since 1993 He was a Guest Researcher at Georgia Institute of

Tech-nology in 1979 and at the University of California/Santa Barbara

in 1990, 1991, and 1997 (some months each) His research

inter-ests include digital signal processing, filters and filter banks,

spec-tral analysis, and speech-signal processing (combined source and

channel coding, enhancement, modeling, and quality assessment)

He is a Member of the IEEE (SM), EURASIP (Secretary 1988–1994,

President 1994–1998), ITG, DEGA, and ASA